Add os.process_id

CHANGELOG.md

@@ -41,6 +41,7 @@ The Koto project adheres to
     - Supports checking if (e.g.) `io.stdin()` is connected to a terminal.
   - `os.command`
     - Supports executing and spawning system commands.
+  - `os.process_id`
   - `random.shuffle`
   - `string.repeat`
 - `tuple.sort_copy` now supports sorting with a key function, following the 

crates/cli/docs/core_lib/os.md

@@ -29,6 +29,14 @@ check! ...
 Returns a string containing the name of the current operating system, e.g.
 "linux", "macos", "windows", etc.
 
+## process_id
+
+```kototype
+|| -> Number
+```
+
+Returns the ID associated with the current process.
+
 ## start_timer
 
 ```kototype

crates/runtime/src/core_lib/os.rs

@@ -23,6 +23,22 @@ pub fn make_module() -> KMap {
         unexpected => unexpected_args("||", unexpected),
     });
 
+    result.add_fn("process_id", |ctx| match ctx.args() {
+        [] => {
+            #[cfg(target_arch = "wasm32")]
+            {
+                // process::id() panics on wasm targets
+                return runtime_error!(ErrorKind::UnsupportedPlatform);
+            }
+
+            #[cfg(not(target_arch = "wasm32"))]
+            {
+                Ok(std::process::id().into())
+            }
+        }
+        unexpected => unexpected_args("||", unexpected),
+    });
+
     result.add_fn("start_timer", |ctx| match ctx.args() {
         [] => Ok(Timer::now()),
         unexpected => unexpected_args("||", unexpected),

crates/runtime/src/error.rs

@@ -62,6 +62,8 @@ pub enum ErrorKind {
     MissingSequenceBuilder,
     #[error("Missing string builder")]
     MissingStringBuilder,
+    #[error("This operation is unsupported on this platform")]
+    UnsupportedPlatform,
     #[error("An unexpected error occurred, please report this as a bug at https://github.com/koto-lang/koto/issues")]
     UnexpectedError,
 }

koto/tests/os.koto

@@ -1,3 +1,6 @@
+@test process_id = ||
+  assert os.process_id() > 0
+
 @test wait_for_command_output = ||
   output = os.command('echo')
     .args 'testing', 'one', 'two', 'three'